Interface SourceDataLine

A source data line is a data line to which data may be written. It acts as
a source to its mixer. An application writes audio bytes to a source data line,
which handles the buffering of the bytes and delivers them to the mixer.
The mixer may mix the samples with those from other sources and then deliver
the mix to a target such as an output port (which may represent an audio output
device on a sound card).

Note that the naming convention for this interface reflects the relationship
between the line and its mixer. From the perspective of an application,
a source data line may act as a target for audio data.

A source data line can be obtained from a mixer by invoking the
getLine method of Mixer with
an appropriate DataLine.Info object.

The SourceDataLine interface provides a method for writing
audio data to the data line's buffer. Applications that play or mix
audio should write data to the source data line quickly enough to keep the
buffer from underflowing (emptying), which could cause discontinuities in
the audio that are perceived as clicks. Applications can use the
available method defined in the
DataLine interface to determine the amount of data currently
queued in the data line's buffer. The amount of data which can be written
to the buffer without blocking is the difference between the buffer size
and the amount of queued data. If the delivery of audio output
stops due to underflow, a STOP event is
generated. A START event is generated
when the audio output resumes.

Method Detail

open

Opens the line with the specified format and suggested buffer size,
causing the line to acquire any required
system resources and become operational.

The buffer size is specified in bytes, but must represent an integral
number of sample frames. Invoking this method with a requested buffer
size that does not meet this requirement may result in an
IllegalArgumentException. The actual buffer size for the open line may
differ from the requested buffer size. The value actually set may be
queried by subsequently calling DataLine.getBufferSize().

If this operation succeeds, the line is marked as open, and an
OPEN event is dispatched to the
line's listeners.

Invoking this method on a line which is already open is illegal
and may result in an IllegalStateException.

Note that some lines, once closed, cannot be reopened. Attempts
to reopen such a line will always result in a
LineUnavailableException.

open

Opens the line with the specified format, causing the line to acquire any
required system resources and become operational.

The implementation chooses a buffer size, which is measured in bytes but
which encompasses an integral number of sample frames. The buffer size
that the system has chosen may be queried by subsequently calling
DataLine.getBufferSize().

If this operation succeeds, the line is marked as open, and an
OPEN event is dispatched to the
line's listeners.

Invoking this method on a line which is already open is illegal
and may result in an IllegalStateException.

Note that some lines, once closed, cannot be reopened. Attempts
to reopen such a line will always result in a
LineUnavailableException.

write

int write(byte[] b,
int off,
int len)

Writes audio data to the mixer via this source data line. The requested
number of bytes of data are read from the specified array,
starting at the given offset into the array, and written to the data
line's buffer. If the caller attempts to write more data than can
currently be written (see available),
this method blocks until the requested amount of data has been written.
This applies even if the requested amount of data to write is greater
than the data line's buffer size. However, if the data line is closed,
stopped, or flushed before the requested amount has been written,
the method no longer blocks, but returns the number of bytes
written thus far.

The number of bytes that can be written without blocking can be ascertained
using the available method of the
DataLine interface. (While it is guaranteed that
this number of bytes can be written without blocking, there is no guarantee
that attempts to write additional data will block.)

The number of bytes to write must represent an integral number of
sample frames, such that:

[ bytes written ] % [frame size in bytes ] == 0

The return value will always meet this requirement. A request to write a
number of bytes representing a non-integral number of sample frames cannot
be fulfilled and may result in an IllegalArgumentException.

Parameters:

b - a byte array containing data to be written to the data line

len - the length, in bytes, of the valid data in the array
(in other words, the requested amount of data to write, in bytes)

off - the offset from the beginning of the array, in bytes

Returns:

the number of bytes actually written

Throws:

IllegalArgumentException - if the requested number of bytes does
not represent an integral number of sample frames,
or if len is negative